Low Temperature Storage of Corms Extends the Flowering Season of Saffron (Crocus sativus L.)

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1 Low Temperature Storage of Corms Extends the Flowering Season of Saffron (Crocus sativus L.) R. Amooaghaie Department Biology Shahrekord University Iran. Keywords: environmental factors, flower initiation Abstract Conditions for the cold- storage of saffron crocus (Crocus sativus L.) corms delay flowering have been characterized. Storage of corms at ºC after flower initiation resulted in a time-dependent abortion of those flowers already initiated. The more advanced the stage of flower initiation at the beginning of cold- storage, the faster the rate of flower abortion. Overall, no benefit resulted from cold- storing corms after flower initiation. Corms stored in the cold before flower initiation, formed flowers when incubated after storage at 1-3 ºC. The number and size of flowers formed, and the yield of spice saffron per corm, depended both on the duration and condition and conditions of cold- storage. Storage at freezing temperatures ( or -1 ºC) damaged the corms. Flowering could be induced in corms stored between 1- ºC. Within this range, temperature had little effect on the subsequent behaviour of corms. Flower number and flower size decreased gradually with increasing duration of cold- storage. Corms lifted after leaf- withering, and stored at ºC in for 6 d, could be forced to flower from early November until the end of December with the same yield of spice saffron as non cold- stored corms. Flowering could be further delayed until May by extending the duration of cold-storage, but this delayed flowering resulted in a significant reduction in spice saffron yield. INTRODUCTION Saffron crocus (crocus sativus L.) is one of most price plants of Iran. Iranian saffron is autotriploid and probably has common origin with other saffron species that has been cultivated in the Mediterranean basin (Behnia, 1993). Its long scarlet stigmas have been appreciated for flavoring and coloring foods, and are now the highest priced spice in the world (Winterhalter and Straubinger, ). The floral biology of the saffron plant has recently been characterized. Saffron crocus corms have no cold requirement to break dormancy, or to complete flower formation as is often found in geophytes (Dole, 3; Rees, 199). Flowering requires as warmintermediate temperature regime. Flower initiation occurs during early spring to mid- Summer, depending on location (Milyaeva and Azizbekova, 1987; Koul and Farooq, 1984; Greenberg- Kaslasi 1991; Molina et al., 5a). High temperatures are required to release bud dormancy and for flower initiation, which is optimal between 3-7 ºC (Molina et al., 4a; 5). Flower emergence occurs in Iranian saffron at a markedly lower temperature, in the range 1-14 ºC (Abarghooie et al., 1999). Through the combined effects of the timing of corm lifting and the duration of incubation as 3 ºC, Molina et al. (4 b, c) were able to programme the flowering of corms between early September to mid- December. Furthermore, the mean duration of the period of flowering of any batch of corms was 13 d, thus allowing efficient use of the greenhouse and harvesting facilities. In the present paper, we

2 report a further extension of the period of flowering by storing corms at low temperature for Iranian saffron. MATERIALS AND METHODS This study has been performed using Iranian saffron corms (Crocus sativus L.) grown in a traditional saffron production area in Boldaji city. Corms were lifted either by the end of June, immediately after withering of the leaves, or 1 month earlier (referred to here as early- lifted corms ). Shortly after lifting, the replacement corms were separated from the remains of the mother corm, cleaned, dipped in a fungicide solution (.1% Prochloraz) and dried. Flower formation was initiated by incubating the corms in the dark at 3 ºC at a relative humidity of 8± 1 %. After incubation at 3 ºC, for periods recorded for each experiment in the results section, corms were covered with a 4-5 cm-deep layer of expanded clay, watered and incubated at 14 ºC for flower emergence. During flowering, light was provided by fluorescent lamps with an 8 h/16 h photoperiod (light/ dark) at a photon flux density of mol m - s -1. Low temperature storage of the corms was performed either directly after lifting (and therefore before flower initiation), or after incubation at 3 ºC to initiate flower formation. In separate experiments, we tested several storage temperatures (from -1 to ºC). Values for these parameters are presented for each experiment in the Results section. During low temperature storage, corms were kept uncovered in the same trays used for flower induction and flowering. Relative humidity was set to 8± 1 %. At the time of flower opening, the stigmata were separated manually and dried under an infra-red lamp to constant weight to determine spice saffron yield. The significance of the differences was tested by ANOVA. When appropriate, mean separation was performed using the lowest significant differences (P <.5). RESULTS Effect of the Temperature of Storage The effect of four temperatures of storage, namely -1,, 1 and ºC, on the flowering behavior of corms stored was determined in early- lifted corms and in corms lifted after leaf withering. The corms used in this experiment were lifted on June and incubated for 8 d at 5 ºC. The corms were then incubated at 15 ºC for d before starting low temperature storage. Low temperature storage at-1,, +1 or + ºC for -6 d was performed. Corms stored at -1 ºC and ºC produced no flowers, but corms stored at 1 ºC or ºC produced most flowers (Fig. 1). Low temperature storage resulted in a marked reduction in saffron spice yield per flower, which increased with the duration of storage (Fig. ). Effect of the Duration of Low Temperature Storage The effect of the duration of low temperature storage on subsequent flower formation was determined using corms lifted on June. At this point, corms were stored at ºC in durations: 6, 1, 14, 18 days. After low temperature storage, the flowering behaviour of the corms was determined. Corms from the same batch where incubated at 3 ºC for -1 d directly after lifting. Upon transfer at 14 ºC, after 4-1 d incubation, these corms formed.5 ±.9 flowers corm, and yielded 8.7 ±.1 mg of spice saffron per flower. When 18-days corms were forced directly at 14 ºC after low temperature storage, they formed no flowers. Flower formation required a previous incubation at 3 ºC after storage. Incubation at this temperature for

3 between 4 and 1 d ensured formation of the maximum number of flowers (Fig. 3). Flower development (Fig. 4 during incubation at 3 ºC, occurred faster in corms previously stored at low temperature for 6-14 d than in freshly harvested corms incubated directly at 3 ºC. A longer duration of cold storage resulted, a slight delay in flower emergence (Fig. 4) and a reduction both in the number of flowers formed (Fig. 4) and in the weight of spice per flower (Fig. 5). The duration of incubation at 3 ºC for optimal flower formation was not affected by the duration of the low temperature storage between 4-1 d (Fig. 3). Effects of storage at ºC on the yield parameters of corms is presented in figure 5. Sixty d of storage had no significant effect on the number of flowers and saffron yield compared to corms that were not stored at low temperature. Corms stored for 6 d flowered from early November until the end of December, depending on the duration of incubation at 3 ºC (from 4 to 1 d; Fig. 3). The yield of saffron spice was in the range mg corm -1 (Fig. 5). Longer low temperature storage allowed flowering until early January, but resulted in a significant reduction in saffron yield (Fig. 5). DISCUSSION In most experiments, low temperature storage resulted in a reduction in the number of flowers formed and or flower size (saffron spice yield). This reduction in flower formation was clearly demonstrated when corms stored at low temperature before flower initiation were forced to sprout at 14 ºC. Usually they did not flower (average number of flowers was. per corm; Fig. 5), while freshly- lifted corms forced directly at 14 ºC without prior incubation at 3 ºC usually formed one flower (Molina et al., 4c; 5b). The reduction in flower number and size caused by low temperature storage depended critically on the developmental stage of the corms at the beginning of storage, and on the conditions and duration of storage. These parameters affected flower number and flower size differentially (Molina et al., 5a). Attempts to expand the low temperature storage of these corms using freezing temperatures ( and -1 ºC) that proved effective in Tulipa (Inamoto et al., ) and Lilium (Koike and Imanishi, 1993; Ikeda, 1997; Lee and Rot, 1) resulted in much faster flower abortion. Crocus corms were very sensitive to freezing temperatures. Flower loss was substantially delayed when low temperature storage was applied to corms that had not reached the flower formation stage. These corms needed additional incubation at 3 ºC to initiate flowers after cold storage (Fig. 3). In conclusion, our experiments demonstrate that flowering could be delayed by storing corms for up to 6 d at 1- ºC before flower initiation. In some experiments, this cold storage caused no significant loss of saffron production compared to nonstored corms (Fig. 5). A small, albeit significant, reduction in the number of flowers occurred occasionally. The delay in flowering, compared to non cold- stored corms, was smaller than the duration of the cold storage. Upon transfer to 3 ºC, cold- stored corms grew faster, and formed flowers earlier (Fig. 4) than freshly harvested corms. This apparently faster growth after cold-storage may have resulted from meristem growth during cold- storage (Molina et al., 5). By varying the duration of incubation at 3 ºC for flower initiation (from 4-1 d; Fig. 3), the flowering of these cold- stored corms may be programmed between early November and the end of \December. The number of flowers formed (.1 per corm) and the yield of spice saffron per flower (8.4 mg) were similar to those reported for freshly- lifted corms of the same size incubated directly at 3 ºC (.5 flowers per corms, and 8.1 mg of

4 saffron spice per flower. These results confirmed those obtained by Molina et al. (5a) on the effects of incubation at low temperature on the time of flowering. Further extension of the period of flowering may be achieved by increasing the duration of cold- storage, but only with a significant loss in spice saffron yield per com compared to the non-stored corms (Fig. 5). Under some conditions, however, this further extension of the flowering period might be economically rewarding. Literature Cited Abarghooie, H. Gholavand, A. Mazaheri, D. Noormohammadi, G.H. and Sanaeie, M The effect of temperature on the flowering and potential yield of Iranian saffron accessions. J. Struc. Res. (Iran). 49: Behnia, M Saffron agriculture. Tehran university publisher, Iran. 36 p. Dole, J. M. 3. Research approaches for determining cold requirements for forcing and flowering of geophytes. Hor. Sci., 38: Greenberg-Kaslasi, D Vegetative and reproductive development in the saffron croucus (Crocus sativus L.). M.Sc, Thesis, the Hebrew University of Jersalem, Istael. [Queted by Ncgbi (1999)]. Ikeda, Y, A system for year- round flowering of Lilium rubellum 'Bakder' by manipulating chilling temperatures, storage duration, and planting time. Journal of the Japanese Society for Hort. Sci. 66: Iminish, H Freesia. In: The physiology of flower Bulbs. (De Hertog, A. and Le Nard, M.Eds.). Elsevier, Amsterdam, The Netherlands Inamoto, K., Sakoda, S., Doi, M. and Manishi, H.. Analysis of effects of temperature and duration of bulb storage on the distribution of dry matter in tulip grown hydroponically. Journa. Of the Japanese Society for Hort. Sci. 69: Koike, Y. and Imanishi, H Long-term freezing storage of bulbs to retard flowering in Asiatic hybrid lilies. Journal of the Japanese Society for Hort. Sci. 6: Koul, K.K. and Farooo, S Growth and differentiation in the shoot apical meristem of the saffron plant (Croucs sativus L.). J. Indian Bot. Soc. 63: Lenard, M. and Dehertog, A.A Tulipa. In: The physiology of flower Bulbs. (De Hertog, A. and Le Nard, M., Eds.). Elsevier, Amsterdam, The Netherlands Lee, J.S. and Roh, M.S. 1. Influence of frozen storage duration and forcing temperature on flowering of oriental hybrid lilies. Hort. Sci. 36: Milyaeve, E.L. and Azizibekova, N.S.H Cytophysiological changes in the course of developments of stem apices of saffron crocus. Soviet plant physiology, 3:7-33. Molina, R.V., Garcia-Luis, A., Coll, V., Campos, C.,Valro, M., Navaroo, Y. and Guardiola, J.L. 4a. Flower formation in the saffron crocus (Crocus sativus L.). The role of temperature. Acta Hort. 65: Molina, R.V., Garcia-Luis, A., Valero, M., Navaroo, Y. and Guardiola, J.L. 4b. Extending the harvest period of saffron. Acta Hort. 65:19-3. Molina, R.V., Valero, M., Navarro, Y., Garc, A, and Guardioloa, J.L. 4c. The effect of time of corm lifting and duration of incubation at inductive temperature on flowering in the saffron plant (Crocus sativus L.). Scientia Hort. 13: Molina, R.V., Valero, M., Navarro, Y., Garc, A. and Guardioloa, J.L. 5a. Low temperature storage of corms extends the flowering season of saffron (Crocus sativus L.). J. Hort. Sci. Biotech. 8:

5 Molina, R.V., Valero, M., Navarro, Y., Guardiola, J.L. and Garcfa-Luis, A. 5. Temperature effects on flower formation in saffron (Crocus sativus L.). Scientia Hort.13: Negbi, M Saffron cultivation: past, present and future prospects. In: saffron. Crocus sativus L. (Negbi, M., Ed.). Harwood Academic Publishers, Australia Rees, A.R Ornamental Bulbs, Corms and Tubers. CAB International, Wallingford, U.K Winterhalter, P. and Straubinger, M.. Saffron. Renewed interest in an ancient spice. Food Rev. Int. 165:39-59.

6 Flowers per corm low temperature storage(d) Fig. 1. The effect of temperature of storage (-1,, 1, ºC) on the number of flowers per corm 1 saffron per flower (mg) low temperature storage (d) Fig.. The effect of duration of low temperature of storage (º C) on the weight of saffron per flower

7 No. Flowers per corm incubation at 5 c 6 d 1 d 14 d 18 d Fig. 3. Effect of the duration of incubation at 3 ºC on flower formation in corms previously stored at ºC for 6, 1, 14,18 days. days at 14 C for flower emergence y = x R =.974 y = -.656x R = incubation at 3 C Fig. 4. Relationship between the duration (in d) of incubation at 3 ºC and the number of d required at 14 ºC for flower emergence, for corms incubated, 6,1, 14, 18 days of storage at ºC.

8 1 saffron spice per flower (mg) d 1 d 14 d 18 d 5 incubation at 5 C (d) saffron spice per corm (mg) d 1 d 14 d 18 d incubation at 3 C (d) Fig. 5. Effect of the duration of incubation at 3 ºC on saffron spice (mg) per flower and weight of saffron spice (mg) per corm previously stored at º C for 6, 1, 14, 18 days.

Regression Models for Saffron Yields in Iran

Regression Models for Saffron ields in Iran Sanaeinejad, S.H., Hosseini, S.N 1 Faculty of Agriculture, Ferdowsi University of Mashhad, Iran sanaei_h@yahoo.co.uk, nasir_nbm@yahoo.com, Abstract: Saffron